In communication systems that employ adaptive modulation, the quality of a signal received by a reception device (received signal quality such as signal to noise ratio (SNR), error vector magnitude (EVM) is judged based on a threshold to determine whether it is allowed to change a communication rate by changing a modulation scheme.
In general, signal distortion significantly influences demodulation in high-rate communications. The distortion increases as transmission power is increased. In order to reduce the signal distortion, some transmission devices decrease the transmission power in response to an increase in communication rate. Therefore, in some cases, received power is decreased after the communication rate is changed.
Patent Document 1 describes a technology of controlling, when multiple terminals are connected to a base station in a spatial multiplexing manner, the uplink transmission power of the terminals according to the propagation environments.    Patent Document 1: JP 2003-244070 A